Powerpoint to help with unit 32 M2 and D2

1. Powerpoint to help with unit 32 M2 and D2 M2: Explain chemical techniques and how they work D2: Evaluate the chemical techniques (when its appropriate to use them and pros/cons)

2. Chromatography This is used to separate out components in a mixture • paper • column • thin layer (TLC) • gas (GC) • high performance liquid (HPLC)

3. Paper chromatography Stationary phase: Filter paper strip Mobile phase: Liquid solvent

4. Paper chromatography • A dot of mixture (e.g. ink with a mixture of dyes) is placed on filter paper/chromatography paper. • The paper is then placed in a beaker of solvent so that the paper absorbs the solvent. • The solvent will then dissolve the mixture and carry the components of the mixture up the filter paper. • More soluble components will be carried up the paper further than the less soluble components. • You can calculate the Rf values and then compare it to literature values

5. Paper chromatography • It can be used to identify what is in a mixture of unknown components • It is cheap, quick and easy to use • It cannot be used to determine the concentration of the unknown components • Some substances can have the same or similar Rf values • You need to know what the Rf value of a chemical is if you suspect that a component may be that particular chemical

6. Thin layer chromatography Stationary phase: Glass plate Mobile phase: Liquid solvent

7. Thin layer chromatography • A dot of mixture (e.g. ink with a mixture of dyes) is placed on a glass plate lined with silica. • The glass plate is then placed in a beaker of solvent so that the glass plate absorbs the solvent. • The solvent will then dissolve the mixture and carry the components of the mixture up the glass plate. • More soluble components will be carried up the paper further than the less soluble components. • You can calculate the Rf values and then compare it to literature values

8. Thin layer chromatography • It can be used to identify what is in a mixture of unknown components- usually organic mixtures like drugs (e.g. the components of a sample of aspirin) • It is cheap, quick and easy to use • It can separate out more components than paper chromatography • It cannot be used to determine the concentration of the unknown components • Some substances can have the same or similar Rf values • You need to know what the Rf value of a chemical is if you suspect that a component may be that particular chemical

9. Column chromatography Stationary phase: silica beads Mobile phase: liquid solvent (usually organic solvent)

10. Column chromatography

11. Column chromatography • It can be used to identify what is in a mixture of unknown components- usually charged particles like metal ions • It is cheap, quick and easy to use • It can separate out more components than both thin layer and paper chromatography • It cannot be used to determine the concentration of the unknown components • It is can be more difficult to separate out the components into the different beakers/flasks

12. high performance liquid chromatography Stationary phase: silica beads Mobile phase: liquid solvent (usually organic solvent)

13. high performance liquid chromatography • A chromatography column is connected to a vacuum pump. • The column is filled with solvent and silica • The tap is opened to allow separated out components to flow out into a beaker/flask • The vacuum pump creates how pressure that is used to push the solvent and the components down the column

14. high performance liquid chromatography • It can be used to identify what is in a mixture of unknown components- usually charged particles like metal ions • It is gives more precise and accurate separation that column chromatography. • It can separate out more components than both thin layer and paper chromatography • It cannot be used to determine the concentration of the unknown components • The equipment set up involves vacuum pump which can make the technique more complicated for some people

15. Gas liquid chromatography Stationary phase: Liquid lined on the capillary tube Mobile phase: inert carrier gas

16. Gas liquid chromatography • This involves an oven filled with a long spiral tube that has been lined with a liquid. • A small amount of an unknown mixture is injected into the oven. The mixture is then vaporised (changes into a gas). • An inert gas is used to carry the mixture through the tube in the oven. • Different components will be carried through the tube in the oven at different speeds- so different components will leave the oven at different times. • At the end of the oven is a detector that measures the retention times of each component (time taken for component to leave the oven)

17. Gas liquid chromatography • This is mainly used to analyse bodily fluids such as urine tests for athletes. • It can be used to determine unknown substances AND their concentrations. • The oven required for this is relatively expensive • You need to know what the retention times of known samples are before you can interpret the retention times of the unknown substances analysed in this technique

18. Spectrometry: instrumental techniques This involves using machines/computers to analyse a sample of chemicals • mass spectrometry • infrared • Ultraviolet • colorimetry

19. Colorimetry

20. Colorimetry • The substance or solution is placed into the sample holder of the colorimeter • A bulb is used to provide a beam of white light • A monochromator acts as a filter and is used to allow the selected wavelength of light to pass through the sample • A sensor then detects how much light has been absorbed by the sample. • More concentrated samples will absorb more light. Less concentrated samples will absorb less light

21. Colorimetry • This can be used to determine the concentration of a poison or an illegal/banned substance in liquids • It is a relatively easy and cheap method to carry out • It only works in coloured solutions (solutions where the concentration affects the intensity of the colour of the solutions) • It cannot be used to determine the identity of unknown substances • You need to select the appropriate wavelength of light to use

22. Ultraviolet

23. Ultraviolet • The substance or solution is placed into the sample holder of the UV spectrophotometer • A bulb is used to provide a beam of UV light which passes through a slit • A monochromator is made up of a dispersion device which spreads out the UV rays and then an exit slit which allows only the selected wavelength of UV rays to pass through onto the sample • A sensor then detects how much UV rays have been absorbed by the sample. • More concentrated samples will absorb more UV rays. Less concentrated samples will absorb less UV rays

24. Ultraviolet • This can be used to determine the concentration of a poison or an illegal/banned substance in liquids • It is can be used on colourless solutions • It cannot be used to determine the identity of unknown substances • You need to select the appropriate wavelength of UV ray to use

25. Mass spectrometry The sample is vaporised (changed into a gas) and injected into the machine. Then four main stages take place

26. Mass spectrometry • Ionisation: The sample is bombarded with electrons to change the molecules into positive ions, so that they are able to move around in the machine. • Acceleration: The ions are then accelerated so that they have some kinetic energy. • Deflection: An electromagnet is then used to deflect the ions. Lighter ions are deflected more and heavier ions are deflected less- this leads to separation of ions. • Detection: The separated ions are then detected and their molecular mass is measured. This can then be used to determine the molecular mass of the chemicals in the unknown sample.

27. Mass spectrometry • This is used to determine what chemicals is in an unknown sample (e.g. to determine whether food or drink samples have been spiked with drugs). • It cannot be used to determine the concentration of the chemicals. • Because the spectrometer contains electromagnets then there are health and safety issues- for example people with pacemakers cannot operate the machine

28. Infra-red spectroscopy

29. Infra-red spectroscopy • IR rays pass straight onto the unknown sample. The covalent bonds of the molecules in the unknown sample will then absorb some of the IR rays. • The transmitted rays pass through the chopper which separates the different transmitted rays according to what their wavenumber is. • The IR detector then detects the transmitted waves which then determines the waves that were absorbed by the unknown sample. • Different organic functional groups will absorb different wavenumbers of IR rays. We can analyse the wavenumbers absorbed to determine what functional groups were in the unknown sample

30. Infrared spectroscopy • This is useful for determining if a sample is likely to contain drugs because drugs contain specific organic functional groups. • The spectrum (results) produced from this Infrared spectroscopy is easy to analyse. • The information obtained from an Infrared spectrum is very limited- you must use other analytical techniques with this • It cannot be used on its own to determine the identify of concentration of a chemical

31. Chemical enhancement This involves using chemicals to participate in a chemical reaction which makes invisible evidence become visible • Fingerprints

32. Chemical enhancement of fingerprints Rheumann’s purple

33. Chemical enhancement of fingerprints How ninhydrin reacts with amino acids

34. Chemical enhancement of fingerprints • Ninhydrin spray can show up latent fingerprints that are on porous surfaces. It reacts with the amino acids and water soluble components of sweat that is left behind as a fingerprint. • This can be used to show up “invisible” fingerprints • The reaction can be quite slow (reaction can take a few hours even weeks to fully take place) but it can be speeded up using an incubator

35. Chemical presumptive tests: bodily fluids These are chemical reagent based tests that involve colour changes to confirm the presence of bodily fluids • Blood • Semen • Saliva

36. Chemical presumptive test of blood

37. Chemical presumptive test of blood • Blood contains haemoglobin inside red blood cells. • Haemoglobin can oxidise the reagent luminol into dianion. • When it does the blue chemiluminescent light is released which is visible to the naked eye- even in the dark. • This test will be used if a violent crime is under investigation • Luminol is very sensitive and detects minute traces of blood, so may indicate the presence of blood after an offender attempts to clean up/wash away the evidence. • Luminol is a hazardous toxic chemical and is considered to possibly be a carcinogen.

38. Chemical presumptive test of semen

39. Chemical presumptive test of semen • Semen contains phosphatase enzyme (known as AP) which is an acid secreted by the prostate gland. • AP catalyses the release of sodium naphthylphosphate which results in a colour change from colourless to purple. • This is also known as the acid phosphatase test (AP test). • This test may be used if semen evidence is submitted from rape/sexual assault/abuse cases and provides important evidence of sexual contact. • Semen is commonly recovered from underwear, clothes, bed sheets and vaginal/oral/anal swabs. • The AP enzyme is also present in other biological fluids but in much smaller concentrations, so a positive result must be confirmed in the lab using a microscope to visually identify the presence of sperm cells.

40. Chemical presumptive test of saliva

41. Chemical presumptive test of saliva • Saliva contains DNA and high levels of the enzyme amylase • The enzyme amylase digests starch into glucose • Phadebas is the chemical reagent used to test for the presence of saliva • Phadebasis made up of starch molecules that contain cross links that have a blue colour. If amylase is present then it will break up the blue coloured cross links between the starch molecules • There will be a colour change from blue to colourless

42. Chemical presumptive test of saliva • The saliva test is easy to carry out • Other bodily fluids contain low levels of amylase but they usually have levels that are not in sufficient quantities to react with Phadebas • Phadebas is relatively expensive

43. Toxicology

44. Toxicology • This involves using a range of the chemical techniques to confirm if drugs/poisons or any chemical which is toxic to living systems has been used in a crime. • It usually involves taking a biological sample from a deceased person and then carrying out instrumental/chromatographic/chemical tests to confirm the contents of the biological sample

45. Toxicology • It is usually accurate because it uses a variety of analytical techniques. One chemical technique can be used to confirm the accuracy of other chemical techniques. • It may be easy to “miss” an observation/make an error in judgement and make wrong assumptions which could influence how you conduct other chemical techniques.